1. Field of the Invention
This invention relates to a radiation image recording and read-out apparatus for exposing stimulable phosphor sheets to a radiation passing through object to have radiation image of the object stored therein, exposing the stimulable phosphor sheet to stimulating rays which cause them to emit light in proportion to the stored radiation energy, and detecting and converting the emitted light into electric signals. This invention particularly relates to a radiation image recording and read-out apparatus in which the stimulable phosphor sheets are circulated and reused for recording radiation images.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet comprising the stimulable phosphor is first exposed to a radiation passing through an object to have a radiation image stored therein, and is then scanned with stimulating rays which cause it to emit light in proportion to the radiation energy stored. The light emitted from the stimulable phosphor sheet when the sheet is exposed to the stimulating rays is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image having an improved quality, particularly a high diagnostic efficiency and accuracy. The finally obtained visible image may be reproduced in the form of a hard copy or may be displayed on a cathode ray tube (CRT). In this radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store the radiation image in order to reproduce the final visible image therefrom in a final recording medium. For economical reasons, therefore, it is desirable that the stimulable phosphor sheet be used repeatedly.
Further, with regard to a mobile X-ray diagnostic station such as a traveling X-ray diagnostic station in the form of a vehicle like a bus which is provided with a radiation image recording and read-out apparatus for use in the aforesaid radiation image recording and reproducing system and moves from place to place to record radiation images for mass medical examinations, it is disadvantageous to load such a mobile X-ray diagnostic station with a number of stimulable phosphor sheets, and the amount of the stimulable phosphor sheets which can be loaded on the mobile X-ray diagnostic station is limited. Therefore, it is desired to load the mobile X-ray diagnostic station with stimulable phosphor sheets which can be used repeatedly, store the radiation images of the objects in the stimulable phosphor sheets, transfer the electric image signals read out from the stimulable phosphor sheets into a recording medium having a large storage capacity, such as a magnetic tape, and circulate and reuse the stimulable phosphor sheets for further image recording and read-out operations, thereby to obtain the radiation image signals of many objects. Further, when image recording is conducted continuously by circulating and reusing the stimulable phosphor sheets, it becomes possible to increase the image recording speed in mass medical examinations. This is very advantageous in practical use.
In order to reuse stimulable phosphor sheets as described above, the radiation energy remaining in the stimulable phosphor sheet after it is scanned with stimulating rays to read out the radiation image stored therein should be eliminated or erased by the method as described, for example, in Japanese unexamined patent publication No. 56(1981)-12599 or U.S. Pat. No. 4,400,619. The stimulable phosphor sheet should then be used again for radiation image recording.
From the aforesaid viewpoint, the applicant proposed in Japanese patent application No. 58(1983)-66730 a built-in type radiation image recording and read-out apparatus comprising:
(i) a circulating and conveying means for conveying at least one stimulable phosphor sheet for recording a radiation image thereon along a predetermined circulation path, PA0 (ii) an image recording section positioned on said circulation path for recording a radiation transmission image of an object on said stimulable phosphor sheet by exposing said stimulable phosphor sheet to a radiation passing through said object, PA0 (iii) an image read-out section positioned on said circulation path and provided with a stimulating ray source for emitting stimulating rays for scanning said stimulable phosphor sheet carrying said radiation image stored therein in said image recording section, and a photoelectric read-out means for detecting light emitted from said stimulable phosphor sheet scanned with said stimulating rays to obtain an electric image signal, and PA0 (iv) an erasing section for, prior to the next image recording on said stimulable phosphor sheet for which the image read-out has been conducted in said image read-out section, exposing said stimulable phosphor sheet to erasing light to release the radiation energy remaining in said stimulable phosphor sheet, PA0 (i) a circulating and conveying means for conveying stimulable phosphor sheets for recording a radiation image therein along a predetermined circulation path, PA0 (ii) an image recording section positioned on said circulation path for recording a radiation image of an object in each of said stimulable phosphor sheets by exposing said stimulable phosphor sheet to a radiation passing through said object, PA0 (iii) an image read-out section positioned on said circulation path and provided with a stimulating ray source for emitting stimulating rays for scanning said stimulable phosphor sheet carrying said radiation image stored therein at said image recording section, and a photoelectric read-out means for detecting light emitted by said stimulable phosphor sheet scanned by said stimulating rays to obtain an electric image signal, and PA0 (iv) an erasing section positioned on said circulation path for, prior to the next image recording in said stimulable phosphor sheet for which the image read-out has been conducted at said image read-out section, exposing said stimulable phosphor sheet to erasing light to release the radiation energy remaining in said stimulable phosphor sheet, PA0 (v) inserting n number of said stimulable phosphor sheets onto said circulation path, wherein n denotes a natural number of 3 or more, PA0 (vi) positioning n-2 or more waiting zones between said image recording section and said image read-out section in the advancing direction of said stimulable phosphor sheets, each of said waiting zones keeping waiting one stimulable phosphor sheet in which said radiation image has been stored, and PA0 (vii) positioning n-2 or more waiting zones between said image read-out section and said image recording section in the advancing direction of said stimulable phosphor sheets, each of said waiting zones keeping waiting one stimulable phosphor sheet from which said remaining radiation energy has been released. PA0 (v) inserting n number of said stimulable phosphor sheets onto said circulation path, wherein n denotes a natural number of 3 or more, PA0 (vi) positioning a stack zone between said image recording section and said image read-out section in the advancing direction of said stimulable phosphor sheets, said stack zone keeping n-2 or more stimulable phosphor sheets, in which said radiation images have been stored, waiting in the stacked form, and PA0 (vii) positioning a stack zone between said erasing section and said image recording section in the advancing direction of said stimulable phosphor sheets, said stack zone keeping n-2 or more stimulable phosphor sheets, from which said remaining radiation energy has been released, waiting in the stacked form. PA0 (v) a first sheet retaining section positioned on said circulation path between said image read-out section and said erasing section for retaining said stimulable phosphor sheets before they are sent to said erasing section, and PA0 (vi) a second sheet retaining section positioned on said circulation path between said erasing section and said image recording section for retaining said stimulable phosphor sheets after they pass through said erasing section.
whereby said stimulable phosphor sheet is circulated through said image recording section, said image read-out section and said erasing section and reused for radiation image recording.
However, since the built-in type radiation image recording and read-out apparatus is the one proposed from the viewpoint that the apparatus is very convenient, for example, for mounting on a mobile X-ray diagnostic station, it is desirable that the apparatus can conduct continuous image recording and read-out operations at as short an interval as possible and is small.
Also, in the aforesaid built-in type radiation image recording and read-out apparatus, stimulable phosphor sheets are circulated through the image recording, image read-out and erasing steps. In general, among these steps, the time required for the image read-out step is the longest (for example, approximately 45 seconds). Therefore, from the overall viewpoint that the image recording and read-out operations are continuously carried out in a number sufficiently larger than the number of the stimulable phosphor sheets circulated in the apparatus and the image recording interval is averaged, the image recording interval is governed by the time required for the image read-out step and cannot be decreased to intervals shorter than the time required for the image read-out step. However, though the image recording and read-out intervals cannot be decreased to a value shorter than the image read-out time from an overall viewpoint, it would be very advantageous in practice that the apparatus be fabricated to conduct image recording operations continuously without any waiting time from a partial viewpoint, i.e. within the range of a limited number of image recording operations. This is because, when a plurality of image recording operations are conducted for one type of object, for example, in mass medical examinations, it is possible to conduct the image recording operation for the object continuously without waiting time. Though a slightly long time is taken for the apparatus to become ready for the next image recording, no problem arises since time is also required for changing the object. Thus it is possible to conduct image recording in a manner which is advantageous in practice.
The erasing section is the section where the stimulable phosphor sheet is exposed to light. In case of exposure to light, for example, a great amount of light (luminance.times.time) is needed to have the stimulable phosphor sheet practically reusable for image recording. In order to shorten the time required for the image erasure, it is necessary to use an erasing light source of high output power (high luminance), which will however require a large scale apparatus and a large capacity of electric power. Therefore, it is considered advantageous to lower the output power of the light source and elongate the erasing time. In this case, however, the elongated erasing time will still necessitate a long processing time for the entire apparatus, and such processing speed is not sufficiently high.